The subject matter disclosed herein relates to pneumatic systems, and more particularly to pneumatic controllers.
Pneumatic controllers typically are configured with a housing including two abutting chambers, separated from each other via a diaphragm, diaphragm plate and a piston. The diaphragm and piston are movable in the housing in response to pressure differences between the two chambers. A spring is located in the housing to bias the position if the piston, and is supported by a spring seat positioned in the housing. A bolt extends through the spring seat and piston to fix the relationship of the components. To aid in sealing between the chambers, a diaphragm is positioned between the spring seat and the piston.
Over the service life of the controller, the bolt stack up between the diaphragm, piston and spring seat can loosen as a result of the diaphragm compressing. This compression also known as “creep” of the diaphragm, results in a calibration of the controller shifting to outside of predetermined acceptable calibration limits. To prevent the diaphragm creep, a collar is incorporated in the bolt stack, extending through a diaphragm opening, through which the bolt also extends. To accommodate the collar, however, the diaphragm opening is enlarged, resulting in a loss of strength of the diaphragm. The loss of strength can lead to rupture of the diaphragm and loss of function of the controller.